The present invention relates to a variable speed controller of an AC motor for detecting the voltage and current fed from an electric power converter, for resolving the detected values to the respective M-axis components arbitrarily fixed and T-axis components perpendicular to the M-axis components and for executing trans-vector control of the AC motor based on the M-axis components and the T-axis components.
FIG. 31 is a block diagram of a conventional variable speed controller of an AC motor. Referring to FIG. 31, the reference numeral 1 designates an electric power converter such as a PWM inverter, 2 an induction motor as the AC motor, 3 a current detector for detecting a current flowing from the power converter 1 to the induction motor 2, 4 a speed detector including a pulse generator for detecting the rotating speed of the induction motor 2, and 10 a variable speed control circuit.
The variable speed control circuit 10 includes a speed regulator 12 that executes proportional plus integral operation of the difference between the reference speed .omega..sub.r * fed from a reference value generator 11 and the actual speed .omega..sub.r detected by the speed detector 4 and outputs a reference torque current value, i.e., a reference T-axis current value, i.sub.T * of the induction motor 2; a slip frequency operating device 14 that calculates a reference slip frequency .omega..sub.S * based on the output of the speed regulator 12, the reference secondary magnetic flux .phi..sub.2 * fed from the reference value generator 11 and the set secondary resistance R.sub.2 * set from a secondary resistance setting device 13; an adder 15 that outputs a reference primary angular frequency .omega..sub.1 * that is a sum of the reference slip frequency .omega..sub.S * and actual speed .omega..sub..tau. ; an integrator 16 that integrates the reference primary angular frequency .omega..sub.1 * and outputs a reference phase angle .theta.*; a coordinate transformer 17 that executes coordinate transformation of the current detected by the current detector 3 based on the reference phase angle .theta.* to operate an actual M-axis current value i.sub.M, i.e., an M-axis component parallel to the magnetic field of the induction motor 2, and an actual T-axis current value i.sub.T, i.e., a T-axis component perpendicular to the M-axis; a T-axis current regulator 18 that executes proportional plus integral operation of the difference between the reference T-axis current value i.sub.T * and the actual T-axis current value i.sub.T and outputs a reference T-axis voltage value v.sub.T *; an M-axis current regulator 18 that executes the proportional plus integral operation of the difference between the reference M-axis current value i.sub.M * fed from the reference value generator 11 and the actual M-axis current value i.sub.M and outputs a reference M-axis voltage value v.sub.M *; and a coordinate transformer 20 that executes coordinate transformation of the reference T-axis voltage value v.sub.T * and reference M-axis voltage value v.sub.M * based on the reference phase angle .theta.* and generates a reference primary voltage value v.sub.1 * fed to the electric power converter 1.
The variable speed control circuit 10 of FIG. 31 executes the so-called slip-frequency trans-vector control. Since the well known techniques are adopted in the constituent devices of the variable speed control circuit 10, the detailed structure of the constituent devices will not be explained.
The slip frequency operating device 14 of the variable speed control circuit 10 operates the following equation (1). EQU .omega..sub.S *=(R.sub.2 *).multidot.(i.sub.T */.phi..sub.2 *)(1)
When the set secondary resistance R.sub.2 * is not identical with the actual secondary resistance R.sub.2, or when the secondary resistance R.sub.2 of the induction motor 2 is unknown, an error is caused in the operated reference slip frequency .omega..sub.S * and an error is also caused in the torque control of the induction motor 2. To obviate this problem, the set value in the secondary resistance setting device 13 is adjusted by the cut and try method while rotating the induction motor 2.
The Japanese Examined Patent Publication (Koukoku) No. H07-67320 discloses a method that obtains the secondary resistance R.sub.2 more exactly in an adaptive state observer based on the detected current value, detected voltage value and actual speed value However, it is necessary for identifying the secondary resistance R.sub.2 by this method to rotate, to accelerate and to decelerate the induction motor.
In view of the foregoing, it is an object of the invention to provide a variable speed controller of an AC motor that obtains the secondary resistance of an AC induction motor by operation without experimentally rotating the induction motor.